<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        .outer{
            height: 500px;
            border-bottom: 10px black solid;
            margin:50px auto;
            /* 外边距重叠问题 */
            overflow: hidden;
        }
    .outer div{
        float: left;
        width: 100px;
        height: 100px;
        border-radius: 50%;
        background-color: #bfa;
        animation: ball 1.5s forwards linear infinite alternate;
    }
    div.box2{
        background-color: yellow;
        animation-delay: .1s;
    }
    div.box2{
        background-color: red;
        animation-delay: .2s;
    }
    div.box3{
        background-color: green;
        animation-delay: .3s;
    }
    div.box4{
        background-color: purple;
        animation-delay: .4s;
    }
    div.box5{
        background-color: pink;
        animation-delay: .5s;
    }
    div.box6{
        background-color: blue;
        animation-delay: .6s;
    }
    div.box7{
        background-color: gray;
        animation-delay: .7s;
    }
    div.box8{
        background-color: yellowgreen;
        animation-delay: .8s;
    }
    /* 创建小球下落的动画 */
    @keyframes ball{
        from{
            margin-top: 0;
        }
        20%,60%,to{
            margin-top: 400px;
            animation-timing-function: ease-in;
        }
        40%{
            margin-top: 100px;
        }
        80%{
            margin-top: 200px;
        }
    }
    </style>
</head>
<body>
    <div class="outer">
        <div class="box1"></div>
        <div class="box2"></div>
        <div class="box3"></div>
        <div class="box4"></div>
        <div class="box5"></div>
        <div class="box6"></div>
        <div class="box7"></div>
        <div class="box8"></div>
    </div>
</body>
</html>